1. Field of the Invention
The present invention relates to a roller or belt conveying device for sheet-like or plate-like workpieces, having low specific gravity such as paper or cardboard, comprising means for changing the orientation of these workpieces about an axis perpendicular to said sheets or plates, as well as to an utilization of this conveying device.
2. Description of the Background Art
Conveying devices, in particular in the manufacturing process, are often associated with means for orienting the conveyed workpieces in a determined position. This is particularly true in the case of folder gluers for the manufacture of boxes or other packaging containers from blanks of paper or cardboard. In fact, in this kind of machine, in which the folding and gluing operations are performed on moving workpieces, it is very important that these workpieces are in predetermined positions in order to carry out these operations. This avoids serious interference with the members that execute the different folding and gluing operations.
To this aim, a conveyor for a so-called two working axis folder gluer machine has been proposed in which two conveyor belts are placed at 90.degree. one from the other, and a transfer element interposed at the vertex of the angle between these two conveyor belts. This transfer element is made up of an intermittently operating conveyor belt, which successively moves the blanks of paper or cardboard from one conveying belt to the other. This method does not permit in-line operation thus appreciably increasing the space requirement, as compared to an in-line machine. In addition, the succession of blanks of paper or cardboard must be regular, since the transferring element must be at a standstill when setting the blank of paper or cardboard and it only starts when this blank of paper or cardboard is well positioned on the transfer element.
Another method for transferring a sheet of paper or cardboard between two conveyor belts arranged at right angle has been proposed in U.S. Pat. No. 5,282,528. In this solution the transfer element consists of two adjacent conveyor belts oriented along a diagonal line connecting two perpendicular conveyor belts. The workpieces to be transferred are moved along this transfer section at a speed which is higher than the speed of the conveyor belts by a ratio that is proportional to the length of a diagonal line considered as the hypotenuse of an imaginary right triangle. With this solution it is possible to operate without maintaining a regular interval between the workpieces to be transferred, but two conveyors arranged at right angle with respect to one another are still required, a 90.degree. rotation of the workpiece is to be made. Consequently, this solution does not solve the problem of the space requirement. Further, if a rotation of 180.degree. has to be executed, two 90.degree. rotation systems in series would be necessary.
Rotating blanks in their plane, during their transport has also been suggested, thus enabling in-line operation. For this purpose, two coaxial rotating members arranged on both sides of the plane of the blanks are used to seize and to turn them. With such mechanism, however, difficulties occur when the blank already includes some folded parts, which have a tendency to unfold. In this case, the operation of rotating members is inconsistent with the presence of continuous guiding elements provided to maintain the parts in a folded position.
A solution intended to meet this difficulty has been proposed in U.S. Pat. No. 3,366,221. The members adapted to turn the blanks consist of perforated plates which are fixed to the conveyor are selectively connected to a suction source. When the perforated plate comes to where the blank has to make a rotation in its plane, it is connected to the suction source, so that by turning, it drives the blank positioned thereon. Therefore, it is possible to position a fixed guide above the path of the blanks to maintain the folded parts in a turned down position. The drawback of this solution is that it is relatively complicated, hence onerous. Also, it requires that the blanks follow one another with constant spacing between them.
It has also been proposed to change the orientation of workpieces having flat contact surfaces by using two conveyors arranged side by side, each separately driven at different speeds, causing a rotation of the workpieces being in contact simultaneously with the two conveyors. To enable two parts of contact surfaces of a common workpiece to be driven at different speeds, obviously, the specific gravity of the conveyed workpieces must be adequate to develop, between each conveyor and the respective contacting surface part, a frictional force great enough to ensure that the portion of the common contacting surface in contact with one conveyor is driven at a different speed than the part in contact with the other conveyor. If that is not the case, problematical sliding occurs and it becomes impossible to determine the rotating angle to an adequate degree of accuracy. In the case of folder gluers for the manufacture of workpieces of paper or cardboard, in particular for the manufacture of boxes or other packaging, the low specific gravity of the blanks of cardboard plates or paper sheets does not actually permit use of a method with two conveyors arranged side by side for turning these plates or sheets around an axis perpendicular to their surface in contact with the conveyor.